Evolutionary approach to the interpretation of sleep function

Evolutionary approach to the interpretation of sleep function seems more promising than the contemporary theories which, in nature, are more utilitarian. The basis of biological approach rest first on the existance of neuronal networks opearting in most primitive (even few cells) organisms. Under an evolutionary pressure, multifunctional neuronal networks developed in response to the need to elaborate more complex tasks relevant to the vital functioning of more complex organisms. As an answer to the need to process the sonsory input a state of calm wakefulness, as a precursor state to the primitive sleep, developed. At a certain point of evolution, coincident with the development of focal vision, the sonsory input relevant to the well-being of the organisms overcame the processing capacity of the existant neuronal networks. A new state of vigilance developed corresponding to the state of primitive sleep in which animals withdrew to the security of an ecological niche. With the advance of focal vision and homeothermy a novel state of vigilance corresponding to 'sleep' developed. The enormous amounts of sensory (specially visual) input relevant for the animal, were moved for processing to the newly developed vigilance state of sleep. This sleep state was able to process memory and perform synaptic strengthening within neuronal networks, without coming into collision with the more vital activities performed at wakefulness (like surveillance of the surrounding, flee reaction, preying, etc). Sleep developed in more complex and higher organisms as an answer to the evolutionary pressures to process the sensory input which would otherwise interfere with the processing capacities of the multifunctional neuronal networks in wakefulness.